Fuel cell block

ABSTRACT

A fuel cell block includes a plurality of channels and pipings and a resulting plurality of connecting and sealed points. Vibrations of the fuel cell block, particularly in vehicles, lead to stress and fatigue of sealed points. This causes a safety problem during operation of the fuel cell block. In order to solve the problem, the fuel cell block includes an end plate, an operating material channel that goes through the end plate and an operating material control device arranged at least partly in the operating material channel. The operating material control device is integrated at least partly into the end plate.

[0001] This application is the national phase under 35 U.S.C. § 371 ofPCT International Application No. PCT/EP02/10373 which has anInternational filing date of Sep. 16, 2002, which designated the UnitedStates of America and which claims priority on European PatentApplication number EP 01123174.3 filed Sep. 27, 2001, the entirecontents of which are hereby incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The invention generally relates to a fuel cell block having anumber of planar fuel cells stacked on top of one another, an end plateand an operating-medium passage which runs through the end plate.

BACKGROUND OF THE INVENTION

[0003] During the electrolysis of water, the water molecules are brokendown into hydrogen (H₂) and oxygen (O₂) by electric current. In a fuelcell, inter alia this operation takes place in reverse. Electrochemicalcombining of hydrogen and oxygen to form water results in the formationof electric current with a high level of efficiency and, if the fuel gasused is pure hydrogen, without the emission of pollutants and carbondioxide (CO₂).

[0004] Technical implementation of the principle of the fuel cell hasled to various solutions, specifically with different types ofelectrolytes and with operating temperatures of between 80° C. and 1000°C. Depending on their operating temperature, the fuel cells areclassified as low-temperature, medium-temperature and high-temperaturefuel cells. These are in turn different from one another by virtue ofdiffering technical implementations.

[0005] For operation, operating media, such as for example the operatinggases, humidification water and cooling water, are fed to a fuel cell.The operating gases used are a hydrogen-containing fuel gas and anoxygen-containing oxidation gas. Examples of the fuel gases which can beused include natural gas, coal gas or pure hydrogen, while the oxidationgas used is generally air or pure oxygen.

[0006] Humidification water is fed to some embodiments oflow-temperature fuel cells, in particular fuel cells with a polymerelectrolyte membrane (PEM fuel cells), the membrane of which has to bekept moist. In this case, the operating gases are heated in a suitabledevice, for example a liquid ring compressor or in humidifier cells, tothe temperature of the fuel cell and saturated with steam.

[0007] A single fuel cell supplies an operating voltage of at mostapproximately 1.1 V. Therefore, a large number of fuel cells areconnected up to form a fuel cell stack which forms part of a fuel cellblock. Connecting the fuel cells in series makes it possible to achievean operating voltage of a fuel cell block of 100 V and above.

[0008] In addition to at least one fuel cell stack, a fuel cell blockgenerally also comprises a humidifying cell stack and what is known asan operating part, also known as the supply part. The humidifying cellstack includes a number of cells in which the operating gases arehumidified with the aid of a membrane. The supply part accommodatesunits such as, for example, pumps, compressors and humidifiers, as wellas equipment such as valves, sensors, electronic monitoring devices,water separators and more.

[0009] The units are connected up by a large number of lines and pipeconnections. These pipe connections are fundamentally susceptible toleaks. In this context, leaks in lines which carry an operating gasrepresent a particular risk to operating safety, since the use ofhydrogen-containing and oxygen-containing operating gases means thatthere is a risk of a fire and possibly even explosions around a leak.When a fuel cell block is being used in a vehicle, an additionaldifficulty is that the fuel cell block is subject to shocks andvibrations.

SUMMARY OF THE INVENTION

[0010] An object of an embodiment of the invention is to provide a fuelcell block which satisfies high safety demands relating to the sealingof the pipe connections even in the event of operation which ischaracterized by vibrations.

[0011] An object may be achieved by a fuel cell block in which,according to an embodiment of the invention, an operating-medium controldevice is at least partially arranged in the operating-medium passageand is at least partially integrated in the end plate.

[0012] An operating-medium control device is to be understood as meaninga device which can be used to influence the quantity or state of anoperating medium or to measure the state of the operating medium (forexample its pressure or temperature). Examples of an influencingoperating-medium control device include a valve, an actuator or a waterseparator, and examples of a measuring operating-medium control deviceinclude a flow monitor or a sensor, such as for example a temperaturesensor, a measured value pick-up, a pressure gauge or a level indicator.

[0013] The various components of a fuel cell block, i.e. the fuel cellstack(s), if appropriate a humidifying cell stack and the supply part,are delimited by at least one end plate, and generally by an end plateon both sides. An end plate is therefore located at one end of the fuelcell block or between two of its components.

[0014] An end plate is generally a stable metal plate which imparts acertain stability to the fuel cell block. An end plate arranged betweentwo components is also known as an intermediate plate. The end platewhich delimits the supply part on the outer side accommodatesconnections for the fuel cell block. Lead-throughs for, for example, theoperating-medium feeds, exhaust gas discharges, lead-throughs fortapping off the electric current which is generated or measurementsignals are incorporated in this end plate, which is also known as theconnection plate.

[0015] An end plate which delimits a fuel cell stack or a humidifyingcell stack is arranged adjacent to in each case the outermostinterconnector plate or separating plate of the stack. Further,depending on the particular embodiment of the fuel cell block, it isalso possible for further components to be located between the outermostinterconnector plate and the end plate.

[0016] An embodiment of the invention includes consideration that thefewer sealing locations and connecting locations in the operating-mediumfeed and discharge lines in the supply part of the fuel cell block, thehigher the operating safety of a fuel cell block. Moreover, anembodiment of the invention includes consideration that the higher themechanical load to which a connecting location, for example a connectionbetween a pipe section and a valve, is exposed, the more susceptiblethis connecting location is to leaks.

[0017] When an operating medium, for example an operating gas, is beingsupplied to the fuel cells, the operating gas is first of all passedthrough the connection plate by means of a connection, then, inside thesupply part, passes through a pipe section before then reaching a valvewhich is used to control the supply of operating gas to the fuel cellstack.

[0018] A reduction in the number of connecting locations inside thesupply part of the fuel cell block is achieved if the valve is arrangeddirectly at the connection plate. This eliminates the pipe sectionbetween connection plate and valve. To allow particularly high loads tobe applied to the connecting location between connection plate andvalve, the valve is partially integrated in the connection plate. By wayof example, a valve seat is formed into the connection plate, and duringassembly of the fuel cell block the valve is inserted fixedly into thisvalve seat. The valve and connection plate therefore form a fixedassembly. The result of this is that the seal within the connectinglocation between valve and connection plate is only exposed to very lowlevels of mechanical load.

[0019] As a result of an operating-medium control device being at leastpartially integrated in an end plate of a fuel cell block, pipe sectionswhich have hitherto been customary between an end plate of this type andan operating-medium control device can be eliminated. As a result, thenumber of connecting locations inside the fuel cell block is reduced.Therefore the operating safety and reliability with regard to leaksinside the fuel cell block are increased.

[0020] The partial integration results in the operating-medium controldevice being rigidly connected to the end plate and a sealing locationbetween the end plate and the operating-medium control device beingarranged inside the end plate. This results in the level of mechanicalload on this sealing location being low, which in turn increases theoperating safety of the fuel cell block.

[0021] This advantage is achieved in particular if the operating-mediumcontrol device is fully integrated in the end plate and is thereforecompletely accommodated by the end plate. Working on the basis of theexample of the valve outlined above, this means that the valve iscompletely incorporated in the end plate and therefore the sealinglocation between connection plate and valve, and also the sealinglocation between valve and a downstream pipe part or a furtheroperating-medium control device, are arranged directly in or at the endplate. As a result, both sealing locations are only exposed to lowlevels of mechanical load.

[0022] If an operating-medium control device is fully integrated in theend plate, it is even possible, under certain circumstances, for thesealing location between end plate and operating-medium control deviceto be dispensed. This occurs because the operating-medium control devicemerges seamlessly into the end plate.

[0023] An embodiment of the invention provides the additional advantagethat, as a result of the at least partial integration of anoperating-medium control device in the end plate, pipe sections andtherefore also space are saved. The supply part and therefore the entirefuel cell block can as a result be of compact design. The assemblyincluding the fuel cell stack and supply part is therefore madeparticularly stable and space-saving by an embodiment of the invention.This is advantageous in particular in vehicles, in which not only themechanical loads but also the limited space available within the vehicleimpose high demands on the fuel cell block.

[0024] A further advantage of an embodiment of the invention is achievedby the operating-medium control device being a water separator. Water(H₂O) is formed when hydrogen (H₂) and oxygen (O₂) are brought togetherin a fuel cell. This product water has to be discharged from the fuelcell.

[0025] The product water is, for example, entrained by the flow ofoperating gas which is passed out of the fuel cells and is not consumedin the fuel cells, and has to be removed from this flow. For thispurpose, operating gas which has not been consumed in the fuel cells ispassed through a water separator, in which the water is separated fromthe operating gas.

[0026] With some types of low-temperature fuel cells, in particular PEMfuel cells, the operating gases are introduced into the fuel cells inhumidified form, since the electrolyte of the fuel cell has to beconstantly kept moist. In the case of a fuel cell block including fuelcells of this type, a water separator is generally also arranged in theoperating-medium feed lines which are used to feed the humidifiedoperating medium to the fuel cells. Humidification water may condenseout inside these pipe feed lines while the fuel cells are operating.

[0027] To ensure that this condensed humidification water does not floodthe fuel cell, a water separator is arranged at least partiallyintegrated in one of the end plates, for example the intermediate plate.The operating gas which has been humidified in the supply part of thefuel cell block is therefore passed through a water separator at or inthe intermediate plate immediately before it enters the fuel cell stack.Moreover, this ensures that the water separator is rigidly connected tothe end plate in a particularly stable and sealed manner.

[0028] It is particularly advantageous for the water separator to becompletely integrated in the end plate. This eliminates the need forsealing locations between pipe connections and the water separatorcompletely. Moreover, this is especially efficient at reducing theoverall volume. The operating medium is introduced into the end plate,excess humidification or product water is removed from the operatingmedium in the water separator in or at the end plate, and then theoperating medium is removed again from the end plate.

[0029] It is expedient for the emptying valve of the water separator tobe completely or partially integrated in the end plate. It is alsoexpedient for the water level indicator to be completely or partiallyintegrated in the end plate. A design of this type effectively avoidsleaks between the emptying valve or water level and water separator.Moreover, the supply part and therefore the fuel cell block may thus beof particularly compact design.

[0030] A further advantage of an embodiment of the invention may beachieved by a connecting passage, which is incorporated in the endplate, for connecting two axial passages which are oriented parallel tothe stack direction of the cells. Axial passages inside a fuel cellstack are used to supply the fuel cell with operating gases and coolingwater and to dispose of these media.

[0031] An example which may be described here is a passage which carriescooling water inside the end plate: depending on the cooling concept ofthe fuel cell stack, by way of example, cooling water is passed out ofthe supply part of the fuel cell block into an axial passage, where itis passed through the fuel cell stack, is distributed from the axialpassage into the fuel cells of the stack, before collecting again in afurther axial passage. At the end of the fuel cell stack, the coolingwater is diverted into a further axial passage, which guides the coolingwater back to the supply part of the fuel cell block.

[0032] The connecting line between the axial passage which collectscooling water and the axial passage which returns the cooling water tothe supply part of the fuel cell block is configured as a passage insidethe end plate which delimits the fuel cell stack with respect to theoutside. In this way, a connecting piece between the two axial passages,together with the sealing locations which are additionally required, isavoided. This increases safety and reliability and saves space. Sincethe metallic end plates impart stability to the overall fuel cell block,their thickness is generally designed to be such that they canaccommodate an operating-medium control device or an operating-mediumpassage without any problems.

[0033] It is expedient for a water separator to be arranged in theconnecting passage and integrated in the end plate. With a configurationof this type, an operating gas from which water is to be removed doesnot have to be passed through additional pipelines to a water separator,but rather has the water removed from it immediately after it exits orimmediately before it enters the fuel cell stack. This results in theadditional advantage that the operating gas is not subject to anycooling in pipelines which are otherwise required and in whichadditional water would be precipitated out by condensation. As a result,the operating gas is kept at the temperature of the end plate and can beintroduced into the fuel cell stack at this readily controllabletemperature.

[0034] It is advantageous for the fuel cell block to include a pluralityof cascaded fuel cell block stages. In this case, the first axialpassage is intended to convey an operating medium out of a fuel cellblock stage and the second axial passage is intended to supply anoperating medium to a subsequent fuel cell block stage. A fuel cellblock which is divided into a plurality of block stages—also known ascascade stages—is particularly suitable for operation in which thehydrogen (H₂) and oxygen (O₂) from the fuel gas and oxidation gas,respectively, are completely consumed inside the fuel cell block. Ablock of this type is used in particular for operation with purehydrogen and pure oxygen, since in this case the operating gases arecompletely consumed and the fuel cell block does not generate anyexhaust gas apart from small quantities of inert gases.

[0035] A fuel cell block of this type is distinguished by a number offuel cell stacks which adjoin one another and are in each case separatedfrom one another, for example, by intermediate plates. The operatinggases and also the cooling water are guided through complex pipes orpassages leading through the individual cascade stages of the fuel cellblock. A large proportion of the pipes in the immediate vicinity of thefuel cell stack can be avoided by the formation of connecting passagesinside one or more end plates at the end or between the cascade stages.This avoids a large number of sealing locations and saves the spacewhich is used for the piping which is otherwise required.

[0036] It is expedient for the operating-medium control device to be avalve, an actuator, a sensor or a flow monitor. All theseoperating-medium control devices can be at least partially integrated inan end plate of a fuel cell block without difficulty. This avoids theneed for sealing locations between an operating-medium control device ofthis type and piping, with the result that the safety and reliability ofthe fuel cell block with respect to faults caused by leaks is increased.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Further advantages, features and details of the invention willbecome evident from the description of illustrated exemplary embodimentsgiven hereinbelow and the accompanying drawings, which are given by wayof illustration only and thus are not limitative of the presentinvention, wherein:

[0038]FIG. 1 shows a fuel cell block with a supply part, a humidifyingcell stack, two fuel cell stacks and five end plates;

[0039]FIG. 2 shows an end plate with integrated water separator;

[0040]FIG. 3 shows a temperature sensor and a valve integrated in an endplate.

[0041] Items which correspond to one another are provided with identicalreference symbols throughout the figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042]FIG. 1 shows a highly simplified and diagrammatic view of a fuelcell block 1 with a supply part 3, a humidifying cell stack 5 a, and twofuel cell stacks 5 b, 5 c comprising PEM fuel cells. The stacks form twocascade stages of the fuel cell block 1. The supply part 3, thehumidifying cell stack 5 a and the two fuel cell stacks 5 b, 5 c are ineach case delimited by an end plate 7 a, 7 b, 7 c, 7 d, 7 e.

[0043] The end plate 7 a is configured as a connection plate. Theconnection plate has a number of current connections 9 for tapping offthe current which is generated in the fuel cell block 1. Moreover, ithas measurement sensor outputs 11 and operating-medium connections 13which are used to supply and discharge operating media to and from thefuel cell block 1.

[0044] The end plates 7 b and 7 b delimit the humidifying cell stack 5a, and the end plates 7 b, 7 d and 7 e delimit the fuel cell stacks 5 band 5 c. The three end plates 7 b, 7 b and 7 d are configured asintermediate plates with a number of operating-medium passages which runthrough the plates but are not shown in the figure. The end plate 7 awhich delimits the fuel cell stack 5 c closes off the fuel cell block 1with respect to the outside.

[0045]FIG. 2 shows the end plate 7 c, which is arranged as anintermediate plate between the humidifying cell stack 5 a and the fuelcell stack 5 b of the fuel cell block 1. A water separator 15 iscompletely integrated in the end plate 7 c, and is incorporated in theend plate 7 c. A connecting passage 17 a opens out into the waterseparator 15 and connects an axial passage of the fuel cell stack 5 b,which runs in the stack direction of the fuel cell stack 5 b, to thewater separator 15.

[0046] While the fuel cell block 1 is operating, oxygen-containingoxidation gas flows through the fuel cells of the fuel cell stack 5 b,collects in the axial passage, connected to the connecting passage, ofthe fuel cell stack 5 b and flows through the connecting passage 17 binto the water separator 15. In the water separator 15, the productwater from the fuel cells of the fuel cell stack 5 b which has beenentrained in the oxidation gas is separated out of the oxidation gas andcollects in the lower part of the water separator 15.

[0047] The oxidation gas from which excess product water has beenremoved then flows onward through the connecting passage 17 a into asecond axial passage, which leads through the fuel cell stack 5 a and tothe fuel cell stack 5 c. The second axial passage is therefore used tosupply the fuel cell stack 5 c with oxidation gas. The connectingpassages 17 a and 17 b can be considered as a single connecting passagewhich connects the first axial passage, which extends into the fuel cellstack 5 b, to the second axial passage, which extends into the fuel cellstack 5 c.

[0048] The water separator 15 includes an operating-medium controldevice 19 which is configured as a water monitor and is completelyintegrated in the end plate 7 c. If the water level of the product waterwhich has collected in the lower part of the water separator 15 risesabove a predetermined level, the water monitor emits a signal to acontrol unit, which is not shown in more detail in FIG. 2 and opensvalve 23 in response to this signal. As a result, the product water isemptied out of the water separator 15 through the drainage passage 21 inthe end plate 7 c.

[0049] An operating-medium control device 24 configured as a flowmonitor is arranged in the drainage passage 21. The flow monitor iscompletely recessed in the drainage passage 21 and is therefore fullyintegrated in the end plate 7 c.

[0050] The water separator 15 is completely integrated in the end plate7 c. As such, there is no need for any connecting locations or sealsbetween the water separator 15 and the connecting passages 17 a and 17 band the drainage passage 21. Moreover, there is no need for any pipingto and from the water separator 15. Thus, routing of the oxidizing agentthrough the water separator 15 can be effected very safely and reliably.Moreover, the water separator and the connecting passages 17 c, 17 b,and also the drainage passage 21 with the flow monitor, are of verycompact design. This reduces the overall volume of the fuel cell block 1as a whole.

[0051]FIG. 3 diagrammatically depicts a section through the end plate 7a configured as a connection plate. The connection plate has a cap 25through which an operating-medium passage 27 extends. Theoperating-medium passage 27 connects one of the operating-mediumconnections 13 to supply devices of the fuel cell block 1 which arearranged in the supply part 3 of the fuel cell block 1. Anoperating-medium control device 29, which is configured as a temperaturesensor, is arranged so as to project into the operating-medium passage27. The temperature sensor is inserted into the end plate 7 a in such away that it is completely integrated in the end plate 7 a. A furtheroperating-medium control device 31, which is designed as a valve, islikewise arranged in the operating-medium passage 27. Theoperating-medium control device 33, which is designed as the actuator ofthe valve, is arranged at the valve and, like the valve, is itselfinserted into the end plate 7 a in such a way as to be likewisecompletely integrated in the end plate 7 a.

[0052] Integration of the operating-medium control devices 29, 31 and 33in the end plate 7 a means that they are very strongly and rigidlyconnected to the end plate 7 a. As a result, there are no mechanicalloads along the sealing surfaces which surround the operating-mediumcontrol devices 29, 31 and 33. This makes it possible to ensure a highdegree of reliability in terms of the leaktightness of these sealinglocations.

[0053] Exemplary embodiments being thus described, it will be obviousthat the same may be varied in many ways. Such variations are not to beregarded as a departure from the spirit and scope of the presentinvention, and all such modifications as would be obvious to one skilledin the art are intended to be included within the scope of the followingclaims.

1. A fuel cell block, comprising: a plurality of planar fuel cellsstacked on top of one another; an end plate; an operating-mediumpassage, running through the end plate; and a water separator, at leastpartially arranged in the operating-medium passage and at leastpartially integrated in the end plate.
 2. The fuel cell block as claimedin claim 1, wherein the water separator is completely incorporated inthe end plate.
 3. The fuel cell block as claimed in claim 1, furthercomprising: a first and a second axial passage, oriented parallel to astack direction of the cells; and a connecting passage incorporated inthe end plate, for connecting the two axial passages, the waterseparator being arranged in the connecting passage and integrated in theend plate.
 4. The fuel cell block as claimed in claim 3, furthercomprising: a plurality of cascaded fuel cell block stages, wherein thefirst axial passage is provided for the purpose of conveying operatingmedium out of one cascade stage, and the second axial passage isprovided for supplying operating medium to a subsequent cascade stage.5. A fuel cell block, comprising: a plurality of planar fuel cellsstacked on top of one another; an end plate; an operating-medium passagerunning through the end plate; and at least one of a water monitor, aflow monitor, a sensor, a valve and an actuator, at least partiallyarranged in the operating-medium passage and at least partiallyintegrated in the end plate.
 6. The fuel cell block as claimed in claim2, further comprising: a first and a second axial passage, orientedparallel to a stack direction of the cells; and a connecting passageincorporated in the end plate, for connecting the two axial passages,the water separator being arranged in the connecting passage andintegrated in the end plate.
 7. The fuel cell block as claimed in claim6, further comprising: a plurality of cascaded fuel cell block stages,wherein the first axial passage is provided for the purpose of conveyingoperating medium out of one cascade stage, and the second axial passageis provided for supplying operating medium to a subsequent cascadestage.
 8. The fuel cell block as claimed in claim 5, wherein the atleast one of a water monitor, a flow monitor, a sensor, a valve and anactuator is completely incorporated in the end plate.
 9. The fuel cellblock as claimed in claim 5, further comprising: a first and a secondaxial passage, oriented parallel to a stack direction of the cells; anda connecting passage incorporated in the end plate, for connecting thetwo axial passages, the at least one of a water monitor, a flow monitor,a sensor, a valve and an actuator being arranged in the connectingpassage and integrated in the end plate.
 10. The fuel cell block asclaimed in claim 9, further comprising: a plurality of cascaded fuelcell block stages, wherein the first axial passage is provided for thepurpose of conveying operating medium out of one cascade stage, and thesecond axial passage is provided for supplying operating medium to asubsequent cascade stage.
 11. A fuel cell block, comprising: a pluralityof fuel cells; an end plate; an operating medium channel, runningthrough the end plate; and means for controlling an operating medium inthe operating medium channel, the means being at least partiallyarranged in the operating medium channel and at least partiallyintegrated in the end plate.
 12. The fuel cell block as claimed in claim11, wherein the means is completely incorporated in the end plate. 13.The fuel cell block as claimed in claim 12, further comprising: a firstand a second axial passage, oriented parallel to a stack direction ofthe cells; and a connecting passage incorporated in the end plate, forconnecting the two axial passages, the means being arranged in theconnecting passage and integrated in the end plate.
 14. The fuel cellblock as claimed in claim 13, further comprising: a plurality ofcascaded fuel cell block stages, wherein the first axial passage isprovided for the purpose of conveying operating medium out of onecascade stage, and the second axial passage is provided for supplyingoperating medium to a subsequent cascade stage.